1. Field of the Invention
The present invention relates to a cooling water temperature controlling apparatus for an internal combustion engine such as an automobile engine.
2. Discussion of Background
Heretofore, a water cooling type cooling apparatus with use of a radiator has been used to cool an internal combustion engine such as an automobile engine. In such cooling apparatus, a thermostat is used to control the temperature of cooling water in such a manner that when the temperature of the cooling water is lower than a predetermined temperature, the cooling water is fed to a bypass passage so that the cooling water is circulated without passing through the radiator.
FIG. 13 is a diagram showing a conventional cooling apparatus. In FIG. 13, a reference numeral 1 designates a cooling water passage formed in a cylinder block for an internal combustion engine, a numeral 2 designates a cooling water passage formed in a cylinder head, which is communicated with the cooling water passage 1 of the cylinder block, and a numeral 3 designates a radiator. The inlet port for cooling water of the radiator 3 is communicated with the cooling water passage 2 of the cylinder head through a radiator inlet passage 4. The outlet port of the radiator 3 is communicated with the cooling water passage 1 of the cylinder block through a radiator outlet passage 5. A numeral 6 designates a cooling water pump placed in the radiator outlet passage 5. A numeral 7 designates a thermostat to control the flow rate of the cooling water supplied to the radiator 3 in correspondence to the temperature of the cooling water, the thermostat 7 being disposed in the radiator inlet passage 4. Further, the thermostat 7 is so constructed as to be entirely closed when the temperature of the cooling water is a predetermined temperature (generally, 80.degree. C.) or lower. A numeral 8 designates a bypass passage for circulating the cooling water by bypassing the radiator when the temperature of the cooling water is lower than a predetermined value, and an end of the bypass passage 8 is connected to the radiator inlet passage 4 at the upstream side of the thermostat 7 by means of a branch portion 9 while the other end is connected to the cooling water pump 6.
The conventional cooling apparatus having the above-mentioned construction operates as follows. When the temperature of the cooling water is relatively low as in a case, for instance, the immediately after of the starting of the engine, the cooling water supplied to the cooling water passage 1 of the cylinder block by means of the cooling water pump 6 is fed from the cooling water passage 2 of the cylinder head to the branch portion 9. At this moment, since the thermostat 7 is entirely closed, the cooling water is not fed to the radiator 3 but is returned to the cooling water pump 6 through the bypass passage 8. Thus, when the temperature of the cooling water is low, the cooling water is circulated without performing a cooling function. When the temperature of the cooling water rises over a set temperature which is determined by the thermostat 7, the thermostat 7 is opened, and the cooling water is fed from the cooling water passage 2 of the cylinder head through the cooling water branch portion 9 and the radiator inlet passage 4 to the radiator 3. Then, the cooling water cooled in the radiator 3 is returned to the cooling water pump 6 through the radiator outlet passage 5 and is again supplied to the cooling water passage 1 of the cylinder block. Thus, the engine is cooled by feeding the cooling water cooled in the radiator 3 to the engine.
In the conventional cooling apparatus, however, the temperature of the cooling water was maintained at a substantially constant temperature (generally, 80.degree. C.) in winter and summer seasons since the temperature was controlled to have a set temperature by the thermostat 7. Accordingly, it was difficult to optimally control the temperature of the cooling water depending on operational conditions of the engine and an outer temperature. For instance, when the temperature of the cooling water is set to have a higher value in view of the performance of a heater and in order to save fuel, the temperature of the cooling water tends to become a higher value in a summer season, whereby a cooling effect to the engine may reduce or the temperature of lubricating oil may increase.
Furthermore, there was a limit in increasing the flow rate of the cooling water since a large pressure loss is resulted when the use of the thermostat is used to control the flow rate of the cooling water. In order to eliminate the above-mentioned disadvantage, there was proposed a cooling water temperature controlling apparatus for an internal combustion engine as disclosed in Japanese Examined Patent Publication Sho 60-20563. In the cooling water temperature controlling apparatus as in the publication, a cooling water passage comprising a first cooling water passage in which a thermostat operable at a high temperature is disposed and a second cooling water passage in which a thermostat operable at a low temperature is disposed, which are parallel to each other, wherein a flow rate controlling valve is disposed in one of the cooling water passages. Although use of the two thermostats allowed to provide various conditions for a set temperature in order to control the temperature of the cooling water, such structure occupied a much space in the engine because of the parallel arrangement of the cooling water passages, and the flow rate controlling valve was needed, whereby it was contrary to the requirements of reducing the size of the cooling water temperature controlling apparatus. Further, in the conventional controlling apparatus, the two thermostats having a large pressure loss are disposed in the cooling water passages, whereby efficiency for supplying a large flow rate was low.
Since the conventional cooling water temperature controlling apparatus as shown in FIG. 13 has a pipe joint and a hose of rubber at the cooling water branch portion 9, work at the time of assembling or inspecting is troublesome because the hose of rubber has to be attached or detached. Further, in the cooling apparatus as shown in FIG. 13, it is difficult to feed entirely the cooling water to the radiator 3 even when the temperature of the cooling water rises beyond a set temperature and the thermostat 7 is entirely opened, because a part of the cooling water flows in the bypass passage 8. Accordingly, efficiency of cooling in the cooling apparatus is low from the viewpoint of the entire cooling system.